Electromagnetic device



D. J. TIMMER El AL 3,022,432

ELECTROMAGNETIC DEVICE Feb. 20, 1962 Filed Nov. 7, 1958 2 Sheets-Sheet 1 DAVID J. TIMMER KENNETH W. PHILBRIOK DAVID W. MOSSBARGER ALFRED M. CATON INVENTORS BYMc W ATTORNEY Feb. 20, 1962 D. J. TIMMER EI'AL ELECTROMAGNETIC DEVICE 2 Sheets-Sheet 2 Filed NOV. 7, 1958 DAVID J. TIMMER KENIETH W. PHILBRICK DAVID W. MOSSBARGER ALFRED M. CATON INVENTORS BY m6 ATToRNEf United States atent Ofitice 3,022,432 Patented Feb. 20, 1962 of Ohio Filed Nov. 7, 1958, Ser. No. 772,467 7 Claims. (Cl. 31037) This invention relates to rotating electromagnetic devices and especially is concerned with a rotary device adapted for intermittent or step-by-step rotation.

Devices of this general type have heretofore been known and this invention concerns itself with an improvement in the ratcheting and locking features of such stepper motors.

It is one object of this invention to provide a compact, simple rotary electromagnetic stepper motor including an improved pawl and ratchet arrangement. A further object of the invention is to provide an improved pawl and ratchet arrangement which may be used with rotating electromagnetic machinery or in other types of apparatus. It is a further object of the invention to provide a stepper motor in which the output shaft is positively held against unwanted motion at all times. These and further objects of the invention will become more readily apparent upon a reading of the specification following hereinafter, and upon an examination of the accompanying drawings in which:

FIGURE 1 is a longitudinal cross sectional view of an electromagnetic device embodying the novel features of the present invention;

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1;

FIGURE 3 is a sectional view similar to FIGURE 2, but showing the device in a different operational position;

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 5;

FIGURE 5 is an end view of the locking assembly of the invention;

FIGURE 6 is a cross sectional view similar to FIGURE 1 but showing a modification of the locking structure of the invention;

FIGURE 7 is a sectional view similar to FIG. 2 but showing the locking structure of FIG. 6; and

FIGURE 8 is a sectional view similar to FIGURE 4 but of the modified locking structure of FIGURE 6 and 7.

Referring to the drawings, and particularly to FIGURE 1, there is illustrated the electromagnetic device 1 of the invention; which comprises, a stator consisting of a case 2 made preferably of ferromagnetic material. The case 2 is an open ended cylinder into which parts of the device can be assembled from both ends.

The case 2 is closed at one end by an end plate or bell 4 and at the other end by another end plate or bell 6, both made of non-magnetic material. Journalled in the end bells at 8 and 10, respectively, and extending between the end bells 4 and 6, is a shaft 12 which is preferably of nonmagnetic material. Over the center portion of the shaft is coaxially mounted a rotor means or rotors 14 and 16. Except when clutched or coupled to the shaft, as is explained in detail hereinafter, the rotors 14 and 16 are free to rotate with respect to the shaft 12.

The two rotors are substantially identical, and further description will be made with reference to the rotor 16, it being understood that rotor 14 is of similar construction. As seen in FIGURE 2, the rotor 16 is provided with three pole means or poles 18, 20 and 22 extending radially outward from the body of the rotor, and preferably formed integral with the rotor. Cooperating with these rotor poles are three stator pole means or'poles 24, 26 and 28 formed inwardly projecting form, and preferably integral with a stator field ring 30. As seen in FIGUREI a stator field ring 30 and a second stator field ring 32 are mounted one on each side of the case 2. These stator rings needv not be made of ferromagnetic material. As clearly shown in FIGURE 1 and with respect to their position along the axis of the shaft 12, the poles on the stator and rotor are in alignment, i.e. They occupy a common plane normal to the shaft 12. The outer radius or face of the rotor poles is slightly smaller than the inner arcuate face of the stator poles, so that when the rotor 16 is rotated clockwise, viewed as in FIGURE 2, only a small air gap will exist between the opposed pole faces. This air gap is indicated at 34 in FIGURE 2.

A suitable coil 40 is mounted in the space formed between the rotor members 14 and 16 as indicated in FIG- URE 1, and by virtue of this structure, when the coil 40 effects a magnetic flux which spans the poles 18 and 24, the poles are attracted, and the rotor 16 is thus rotated clockwise as viewed in FIGURE 2, until the stop member 42 abuts the side of the lever 46 of the locking means described more fully hereinafter.

The rotor is biased by a torsion spring 15 (see FIGURE 1), which is preferably non-magnetic and is suitably mounted at one end to the end bell 4 and at its other end to the rotor member 14. In the unactuated position the rotor is biased so that stop member 44 bears against the lever 48 of the retaining or locking means. The two stop members 42 and 44 are in the form of pins which are' embedded into and suitably aflixed to one of the rotor poles 20.

Coaxially circurnjacent the rotors 14 and 16, there is mounted a coil means in the form of an electric coil 40 which is carried within a spool 41 preferably made of non-magnetic material. Alternately the coil may be encapsulated in a plastic material. The coil assembly may be placed within the case 2 from either direction and the mounting rings 32 and 30 inserted to retain the coil in position. The pins 17 retain the two rotor members 14 and 16 together as an integral unit. Whenever the coil 40 is energized through appropriate wires, an axial flux is established in the rotors 14 and 16 and in the case 2, with the flux path extending between the circumferentially spaced series of rotor and stator poles. This flux draws the poles together, thereby rotating the rotor clockwise as viewed in FIGURE 2.

Means are provided for coupling the rotor to the output shaft 12 so that the output shaft 12 will be rotated in an intermittent or step-by-step fashion. This means for intermittently coupling the rotor to the shaft 12 comprises.

a pin 50 which is mounted on the rotor part 16 and projects outwardly therefrom away from the coil 40.

Mounted on this pin 50 is a pawl member 52 which is in the form of a bell crank. This pawl 52 is biased in a clockwise direction as viewed in FIGURE 2 by a spring 54 which is mounted at one end on a pin 56 which is also afitxed to the rotor member 16, and the spring 54 is" mounted at the other end to a stud 58 which forms part of the bell crank lever 52. The bell crank lever 52 has a face 60 which is adapted to engage into the teeth portions 62 of a ratchet wheel 64, which is pinned or otherwise fixedly mounted to the shaft 12. As the rotor rotates in a clockwise fashion the spring loaded pawl 52 which is in engagement with the teeth 62 of the ratchet wheel 28 will rotate the shaft 12 until the stop pin 42 abuts against the stop lever 46. At this time current is removed from the coil 40 and the spring 15 will return the rotor. to the starting position; the spring loaded pawl 52 will then slide or freewheel over the ratchet wheel 64 until it assumes its previous position upon a tooth 62.

To restrain the output shaft 12 against unwanted rotation at all times, both when the device is in operation and when inactivated, there is provided a locking means 70.

(See FIGURES 4 and 5.) The locking assembly consists of two thin partial plates 72 and 74 which are suitably fastened together and maintained in spaced relationship by a series of spacer members 76, and which form a housing for the latching lever and associated mechanism. As shown more clearly in FIGURE 4, the locking elements comprise two levers 46 and 48 which are pivotally mounted on the thin plate 72 upon pins 78 and 80, respectively. These locking levers 46 and 48 comprise hammer portions 84 and 82, respectively, and also depending abutment extensions 86 and 88, respectively. These abutment extensions 86 and 88 are adapted to cooperate with the pins 42 and 44 mounted upon one of the rotor poles. Also mounted upon the thin wafe plate 72 is the lock or latch member 92 which is generally in the shape of a bell crank. This lever 92 is mounted upon pin 90 and biased downwardly as viewed in FIGURE 4 by a spring 94 which is afiixed at one end to a post 96 embedded in the plate 72 and at the other end to a lug 98 formed upon the lever 92. This lever 92 has an upper anvil portion 180 upon which the hammer levers 46 and 48 may strike'to drive the lever 92 downwardly. The tooth portion 102 of the lever 92 is adapted to latch into the teeth 69 of the ratchet wheel 64 for locking purposes.

In operation, with the unit de-energized, the shaft 12 is prevented from any motion in either direction by both the feed pawl 52 and the locking mechanism. The spring is pre-loaded so that in the inactivated condition of the unit it will still exert an appreciable force tending to rotate the rotor counterclockwise as viewed in FIGURE 2 and drive the stop pin 44 against the depending arm of lever 48. Since lever 48 is pivoted about pin 78, the hammer portion 82 will impinge upon the anvil 100 of the lever 92 and drive it downwardly into locking position upon the ratchet wheel 64. This will prevent any rotation of the ratchet wheel and hence the shaft 12 in either direction. In addition a further locking action is provided by the feed pawl 52 which is urged downwardly into the teeth 62 of the ratchet wheel 64 by the spring 54. The spring 94 performs a similar function upon the lever 92 as above indicated. It is thus seen that in the inactivated position the shaft 12 cannot rotate in either direction. When the coil 4! is actuated and the rotor commences rotation, the stop pin 44 will move out of contact with the lever 48 and hence there will be a lifting of the driving force upon lever 92 to permit the ratchet wheel to be carried forward by the drive pawl 52 to rotate the shaft 12 in the desired manner. When the drive pawl 52 has reached the limit of its travel as viewed in FIGURE 3 the stop pin 42 will have moved into position abutting against arm 86 of lever 46 and driving the hammer portion 84 upon the anvil 100, again forcing lever 92 to seat upon the ratchet wheel 64 and prevent any further forward motion of the rotor and hence, of the drive or the output shaft 12. This will prevent any overdrive of the mechanism, since at the end of its stroke the shaft 12 is again locked against rotation in either direction. Upon discontinuance of the current to the coil 48 the return spring 15 will return the rotor to the position shown in FIGURE 2 and the locking mechanism and drive pawl 52 will prevent overdrive past the return position and positively lock the shaft 12 against motion in either direction until the next stepping cycle.

An alternate arrangement of a positive locking mechanism is shown in FIGURES 6, 7 and 8 wherein a plate 110 is shown which is mounted upon the end bell 6 of a stepper motor similar in all respects to that shown in FIGURE 1 except for the locking mechanism. This locking mechanism also consists of a pair of lever members 146 and 148 which are mounted upon pins 180 and 178 respectively. The pins 178 and 180 are aflixed to or integral with the partial disc 110. These levers 146 and 148 are similarly shaped to the similar levers 46 and 48 of the modification of FIGURE 4 and are provided with the hammer portions 184 and 182, and the depending lug portions 188 and 186. The latch lever 192 is pivotally mounted upon a post 190 which is affixed to the disc and is biased downwardly as viewed in FIGURE 8 by a spring 194 which is afiixed at one end to a post 196 mounted upon disc 110 and at the other end to a lug 198 formed upon the lever 192. The outer portion 206 of the lever 192 constitutes the tooth or latch portion which is embedded into the teeth of the ratchet pawl 64. The lever 192 is forced downwardly by a hammer pin 202 which has an anvil portion 204) juxtaposed to the hammer portions 182 and 184 of the levers 148 and 146 respectively. This pin 202 slides within a hole in a boss 204 formed upon the disc 110.

The operation of this latching mechanism is similar to the operation of the mechanism shown in FIGURES 2 and 3, and it is readily seen that when the stop pin 44 abuts against the lug 188 of lever 148 the hammer portion 182 will be driven upon the anvil 200 of pin 202 thus forcing it downwardly to positively hold the lever 192 into engagement with a tooth of the ratchet wheel 64. At the other end of the travel of the rotor the stop pin 42 will perform a similar function against the lug 186 of lever 146, thus driving the hammer 184 upon the anvil 280 and similarly causing the lever 192 to seat upon a tooth of the ratchet wheel 64.

There is thus described hereinabove a novel stepper motor which provides the desirable function of positively preventing unwanted movement of the output shaft and locking it against any motion at those times in the duty cycle when even a slight displacement would become cumulative and destroy the accuracy of the instrument over a period of time. Although the invention has been described with respect to specific embodiments thereof, it is recognized that various departures and modifications may be made therefrom within the scope of the invention as defined in the appended claims.

What we claim is:

1. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output shaft rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a mag netic field therebetween, said mechanism comprising hammer means movably mounted on said housing, a movably mounted detent means juxtaposed to said hammer means, said shaft being provided with detent receiving means, actuating means mounted upon said rotatably mounted rotor and adapted when in one position to engage said hammer means to drive said detent means into locking engagement with said detent receiving means, thereby locking said shaft against rotation.

2. The device of claim 1 wherein said detent receiving means includes a recess for receiving one end of said detent means, biasing means for yieldingly urging said detent means into said recess, whereby when said actuating means are no longer in engagement with said hammer means said shaft may rotate upon removing said detent means from said recess against the action of said biasing means.

3. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output shaft rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a mag netic field therebetween, said mechanism comprising hammer means including a lever pivotally mounted upon said housing, a movably mounted detent means juxtaposed to said hammer means, said shaft being provided with detent receiving means, actuating means mounted upon said rotatably mounted rotor and adapted when in one position to engage said hammer means to drive said detent means into locking engagement with said detent receiving means, thereby locking said shaft against rotation.

4. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a magnetic field therebetween, said mechanism comprising hammer means including a lever pivotally mounted upon said housing and provided with a hammer portion and a depending lug, a pivotally mounted detent member yieldingly biased towards said shaft and juxtaposed to said lever, said shaft being provided with detent receiving means, actuating means mounted upon said rotatably mounted rotor and adapted when in one position to engage said hammer means to drive said detent means into locking engagement with said detent receiving means, thereby locking said shaft against rotation.

5. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output shaft rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a magnetic field therebetween, said mechanism comprising hammer means including a lever pivotally mounted upon said housing and provided with a hammer portion and a depending lug, a pivotally mounted detent member yieldingly biased towards said shaft and juxtaposed to said lever, said shaft being provided with detent receiving means including a member presenting a circumferential surface having a series of re-entrant portions, a member mounted upon said rotor and adapted when in one position to engage the lug of said lever causing it to pivot and have its hammer portion contact said detent member to drive it into locking engagement with a reentrant portion of said detent receiving means, thereby locking said shaft against rotation.

'6. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output shaft rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a magnetic field therebetween, said mechanism comprising hammer means including a pair of levers pivotally mounted upon said housing, a movably mounted detent means juxtaposed to said hammer means, said shaft being provided wtih detent receiving means, a pair of actuating members mounted upon said rotatably mounted rotor each associated with a lever of said hammer means and alternatively adapted when in one position to engage its said lever to drive said detent means into locking engagement with said detent receiving means, thereby locking said shaft against rotation.

7. Locking mechanism for preventing undesired rotation of the output shaft of an oscillating electromagnetic device comprising a housing enclosing a stator means having at least one pole, an output shaft rotatably mounted in said stator means, rotor means rotatably mounted coaxially circumjacent said shaft and having at least one pole, said poles being mutually circumferentially attracted to each other upon effecting of a magentic field therebetween, said mechanism comprising hammer means including a pair of levers pivotally mounted upon said housing, each lever comprising a hammer portion and a depending lug, a pivotally mounted detent member yieldingly biased towards said shaft and juxtaposed to said levers, said shaft being provided with detent receiving means, a pair of actuating members mounted upon said rotatably mounted rotor each associated with a lever of said hammer means and alternatively adapted when in one position to engage its said lever to drive said detent means into locking engagement with said detent receiving means, thereby locking said shaft against rotation.

References Cited inthe file of this patent UNITED STATES PATENTS 

